Active resistance-capacitance (RC) band-pass filters are commonly used in various radio receiver designs. For example, U.S. Pat. Nos. 5,630,228, 5,862,323, 5,852,722, whose disclosures are incorporated herein by reference, describe receiver configurations that employ active filters.
Some applications use single-ended or unbalanced active filter configurations. For example, Chen describes an unbalanced active RC filter design called a “Sallen and Key” filter, in “The Circuits and Filters Handbook,” CRC Press, December, 2002, section 81.2, pages 2472-2475, which is incorporated herein by reference.
Other applications use balanced, or differential, filter configurations. For example, Banu and Tsividis describe a balanced fifth-order active band-pass filter in “Fully Integrated Active RC Filters in MOS Technology,” IEEE Journal of Solid-State Circuits, volume SC-18, number 6, December 1983, pages 651-64, which is incorporated herein by reference.
In some applications, such as the Banu and Tsividis paper cited above, active filters are implemented in a fully-integrated manner in a radio-frequency integrated circuit (RFIC).